[release/7.0] [SignalR] Unblock user callbacks when waiting for client result

[github-actions]

Backport of #43944 to release/7.0

/cc @halter73 @BrennanConroy

Unblock user callbacks when waiting for client result

This was already an issue with Task returning .On methods, but client results likely makes it more likely to block on the client side

• .NET client blocks other .On handlers but does not block the receive loop
• JS client doesn't block anything, .On handlers for future invokes/sends can still run while blocked on user input, pings/etc. still received and processed
• Java client blocks other .On handlers but does not block the receive loop

Fixes #41996

Customer Impact

@DavidErben writes

Hey guys, I just tried this out with .NET 7 RC1 and the methods are still blocking (like before if one returned a Task). Are there any plans to change this behavior for the official .NET 7 release?

We are using this feature to trigger commands on connected IoT devices. Usually a bunch of commands are triggered simultaneously, so it would be cool if they would run in parallel. But if it is not possible it is not a huge deal either.

Regression?

• Yes
• No

No. But without this fix, client return values are not as usable with the C# and Java clients as they are with the TS/JS client.

Risk

• High
• Medium
• Low

This only affects applications taking advantage of SignalR's new client return feature.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

[halter73]

@Pilchie This issue was identified a while ago, but we're getting early feedback from rc1 that this is an important fix for .NET 7.

I agree this is really important. It makes the C# and Java clients unusable for certain client return scenarios that work just fine with our TS/JS client. This is a relatively simple change that brings the clients in line with each other.

[Pilchie]

Approved for .NET 7 RC2 (pending passing CI).

[halter73]

@dotnet/aspnet-build The OSX template failures are unrelated. This PR fully passed in main already. Can we merge this before branching?

[wtgodbe]

That's fine with me